Field of the Invention
The present invention relates to a gear pump and a gear pump operating method.
Description of the Related Art
For example, in a resin kneading granulator that granulates a kneaded resin into pellet, a gear pump is generally used as a pressure raising device that pressure-feeds a kneaded and melted resin to a screen or an extrusion die located at the downstream side of a kneader. The gear pump is formed so that a pair of gear rotors engaging with each other is provided inside a hollow casing (a pump casing), and is configured to pressure-feed a resin material received into the casing by using the gear rotors.
Incidentally, there is a need to increase the size or the speed of the gear pump in order to improve the productivity of the resin kneading granulator. However, when the gear rotor is increased in size or is rotated at a high speed in this way, heat is easily generated inside the pump, and the components are thermally expanded due to the generated heat. As a result, a gap between a gear rotor and a bearing is narrowed, and hence the smooth rotation of the gear rotor is disturbed.
For this reason, Japanese Patent Application Laid-Open No. 10-141247 discloses a gear pump capable of cooling a gear rotor or a hearing by circulating a cooling medium. In this way, when the gear rotor or the bearing is cooled, the thermal expansion of the components inside the pump may be suppressed. Further, when the components such as the gear rotor or the bearing are heated or cooled, the components extend and contract in a different way, and hence there is a need to adjust the gap between the gear rotor and the bearing.
In order to solve such a problem, Japanese Patent No, 3988258 discloses a technique of adjusting a gap formed between components inside a pump. That is in this technique, a driving shaft of a gear rotor protruding from a driving gear to the outside of a casing is provided with a gap adjustment mechanism that keeps a side clearance between the side surface of the driving gear and the casing so as to be uniform. When the side clearance is kept uniform by the gap adjustment mechanism, the gap between the bearing and the gear rotor disposed inside the pump and connected through the driving shaft is also kept uniform.